Method for prolonging shelf life of fresh milk
Technical Field
The invention relates to the technical field of food processing, in particular to a method for prolonging the shelf life of fresh milk.
Background
The standardized process flow of pasteurized milk is: cleaning and cooling raw milk, sterilizing at low temperature for long time (63 deg.C for 30 min) or at high temperature for short time (72-85deg.C for at least 15 s), and cooling to 2-6deg.C. The sterilization process of pasteurized milk on the market at present comprises (1) pasteurization process of maintaining at 72 ℃ for 15s, and shelf life of 3-7 days; (2) the combined process of centrifugal sterilization and pasteurization at 72 ℃ is adopted, and the shelf life can reach 7-10 days; (3) adopts a steam instantaneous direct heating sterilization mode, and the shelf life can reach 15-20 days. The dairy products treated by the process all need to be stored at low temperature. The former two can ensure the content of active ingredients in the product, but the shelf life is shorter, and the latter can effectively ensure the shelf life of the product, but the loss is higher.
The ultrahigh pressure sterilization technology is to destroy the microbial cell membrane by using pressure (usually 100-1000 MPa), inhibit biochemical reaction, promote DNA denaturation in cells and the like so as to meet the sterilization requirement. The ultrahigh pressure can cause various changes of the morphological structure, the genetic mechanism, the biochemical reaction, the cell membrane and the like of the microorganism, thereby further influencing the physiological function of the microorganism and even causing the original function to be destroyed or irreversibly changed.
The ultra-high pressure sterilization technology can be divided into a static ultra-high pressure type and a dynamic ultra-high pressure type, wherein the static ultra-high pressure type is that an object to be sterilized is placed in a high-pressure container, water or other fluid is used as a pressurizing medium, and the pressure is maintained for a certain time under a certain pressure, so that the protein maintaining the vital activity of microorganisms can be denatured and deactivated, and the aim of sterilization is achieved. The pressure maintaining time has obvious influence on the static ultrahigh pressure sterilization effect, and the higher the pressure is, the better the sterilization effect is, and the pressure above 300MPa can kill common microorganism groups in foods such as bacteria, mold, saccharomycetes and the like. Static ultrahigh pressure sterilization is a very complex process, for example, some bacteria producing buds have high pressure requirements for sterilization effect, high pressure equipment investment is large, the pressure is extremely high, the control and the grasp are difficult, and the industrialization difficulty is large.
The dynamic ultrahigh pressure is to pressurize the articles to be sterilized to a designated pressure point, then evaporate the water or other media permeated into the microbial cells by pressurization to explode by means of instantaneous pressure release or gradient pressure reduction and the like, and the spatial structure of the protein can be destroyed under huge puffing pressure, thereby achieving the aim of sterilization. The basic working principle of the ultra-high pressure jet is that ordinary water or other liquid to be treated is filtered, then the mechanical energy of a power source (a motor) is converted into the pressure energy of the liquid through a specific energy conversion device (a high-pressure pump or a booster), the liquid with huge pressure energy is ejected through a small-hole nozzle, and the pressure energy is converted into kinetic energy, so that high-speed jet is formed. The conversion process from normal liquid to high-speed jet is mainly the jet energy conversion process, the booster is the key for forming the energy accumulation of the liquid, and the nozzle is the key for jet formation.
The invention patent with publication number CN101690515, namely a low-temperature ultrahigh-pressure sterilization method for liquid milk, is characterized in that cold chain liquid raw milk is subjected to a booster, the pressure of the cold chain liquid raw milk is increased to 400MPa from normal pressure, then the liquid milk enters an accumulator to eliminate high-pressure pulsation, then the liquid milk is emitted through a nozzle, the liquid milk is sterilized and homogenized by strong collision of supersonic jet, and the temperature of the liquid milk can reach 70 ℃; finally, the temperature of the sterilized liquid milk is reduced, and aseptic packaging is carried out. The product obtained by the invention can meet the national standard of pasteurized milk, can be beneficial to preserving the nutrient components of cow milk, and can be produced continuously. However, the method has the defect that the temperature of the sample after ultrahigh-pressure jet is low, the number of microbial colonies is large, and the inactivation of alkaline phosphatase and lactoperoxidase cannot be ensured.
Alkaline phosphatase has a slightly higher thermostability than most pathogenic microorganisms in milk, such as tubercle bacillus, listeria, etc. When the milk heat treatment is of sufficient intensity to render the alkaline phosphatase activity test negative, it is indicated that other pathogenic microorganisms are also completely inactivated, and thus the alkaline phosphatase activity indicator is a very important indicator in the dairy industry, which indicates the success or failure of pasteurization of the milk product.
Lactoperoxidase is also a typical heat-sensitive enzyme in cow's milk, and has higher thermostability than endogenous enzymes in other milk. Studies have shown that lactoperoxidase begins to denature during dairy processing under hot processing conditions of 68 ℃/15 s. The activity of the lactoperoxidase is lost by 60-70% in the case of a hot working condition of 74 ℃/15 s. The conditions for complete denaturation were 78℃for 15s, or 74℃for 60s. The activity of lactoperoxidase can mark whether excessive heat processing, heat treatment and the like occur in the pasteurization process, so that more nutrients in milk are lost, and the activity is an important index in the dairy industry.
The conventional raw milk sterilization method can only sterilize, and the alkaline phosphatase in the bacterial body usually has partial activity after sterilization and is not completely inactivated. The inventor finds that the high-temperature and high-pressure process can activate the activity of the enzymes in the bacteria in long-term production practice, so that the sterilization method of raw milk in the prior art can not realize the simultaneous high-efficiency inactivation of the bacteria and the enzymes in the bacteria (such as alkaline phosphatase). The alkaline phosphatase in the cell body can react with the nutrient components such as protein, fat and the like in the raw milk, and the taste of the raw milk is reduced. To solve this problem, a common technical means is sterilization and enzyme deactivation. The sterilization operation and the enzyme deactivation operation can solve the problems theoretically, but in actual operation, it is found that, because the enzyme deactivation requires higher temperature or pressure, if the higher temperature or pressure is selected, the enzyme deactivation can be performed, but new problems occur: other lactoperoxidase and other lactoses in raw milk can be inactivated, and the high temperature and the high pressure destroy the structures of raw milk proteins and fat, so that the raw milk has poor taste due to protein denaturation and fat denaturation, and the high temperature and the high pressure are accompanied with high energy consumption, so that the development requirements of energy conservation and environmental protection of enterprises are not facilitated. Therefore, the conventional thought needs to be changed, and a new sterilization and enzyme deactivation method which solves the main contradiction is sought.
The invention patent with publication number 111528279 discloses a sterilization method of liquid milk, which is to add nisin as a bacteriostatic agent to perform bacteriostasis treatment and homogenization on the liquid milk, and then perform ultrahigh-pressure water jet sterilization treatment. The product obtained by the invention has longer shelf life, and better flavor, color and taste of milk. However, the technology has the defects of complex operation steps, need to control the addition amount of the bacteriostat nisin, high pressure resistance, high technical requirement of a sterilized collection container and high manufacturing cost.
The sterilization mode of raw milk in the prior art has advantages and disadvantages in the aspects of production process, nutritional value, shelf life and the like, and how to obtain fresh milk with both high nutritional ingredients and long shelf life is a problem to be solved in the art.
Disclosure of Invention
The invention aims to overcome various defects of the existing heat sterilization technology, and provides a sterilization method of low-temperature fresh milk, which is suitable for industrial production, has less nutrient loss and remarkably prolonged shelf life, namely a method for prolonging the shelf life of the fresh milk, aiming at the problems that the shelf life of the existing pasteurized milk is too short, the condition requirement of the preservation period is high, the product is easy to deteriorate in shelf life, the high-temperature long-time sterilization nutrient components have larger loss, and simultaneously, the heat sterilization and static ultrahigh-pressure sterilization pressure has high energy consumption and high machine cost.
The invention discovers in the long-term study of the sterilization process of raw milk that the static ultrahigh pressure treatment of liquid milk has the defect of limited effect on killing microorganisms, and the bacterial colony total number is less than 1CFU/ml although the partial killing of the product spores can be realized through low-pressure and high-pressure alternation and cyclic pressurization; the enzyme cannot be completely deactivated, and when the pressure exceeds 400MPa, the protein begins to denature, so that the taste of the cow milk is poor; the ultrahigh pressure equipment investment is larger, the pressure required by sterilization is higher, the requirement on the high pressure resistance of the equipment is higher, the purchase and maintenance cost of the equipment is high, the static ultrahigh pressure technology needs to be subjected to certain pressure-bearing time in a fixed container in the process of sterilizing the cow milk, and the industrialization difficulty is higher.
The invention provides a method for prolonging the shelf life of fresh milk by combining a dynamic ultrahigh pressure technology with other sterilization technologies, which comprises four steps,
the first step: firstly, carrying out degerming and centrifuging treatment on raw milk to remove part of spores and bacteria;
and a second step of: the raw milk is subjected to high-pressure pump energy storage, and high-pressure pulses are removed;
and a third step of: the method comprises the steps of adopting dynamic ultrahigh-pressure jet collision to raw milk, converting mechanical energy of the raw milk into kinetic energy, forming high-speed jet, and heating while the collision releases energy;
fourth step: and (3) carrying out low-temperature heat treatment on the heated raw milk to finish sterilization and enzyme deactivation.
In the first step of the method provided by the invention, the water pressure of the degerming centrifugation is 2-5bar, the inlet pressure is 2-6bar, the outlet pressure is 2-6bar, the compressed air pressure is 6-8bar, the separation temperature is 50-55 ℃, the water pressure is less than or equal to 2.5bar when deslagging, and the separation rotating speed is 4000-7000rpm.
In the second step of the method provided by the invention, before a dynamic ultrahigh-pressure jet collision method is adopted, high-pressure pump energy storage is carried out on raw milk cooled to 2-6 ℃, high-pressure pulses are removed, and the high-pressure energy storage pump uses 38.5kW/380V alternating current, and the pressurizing time is less than or equal to 30s. The invention discovers that when the pressurization time is not more than 30s, the pressure stability can be ensured, thereby effectively ensuring the improvement of the sterilization efficiency.
In the second step of the method provided by the invention, the total pressure of the dynamic ultrahigh pressure jet is 50-350MPa, preferably 150-250MPa, more preferably 200MPa; the secondary pressure of the dynamic ultrahigh pressure jet is 5-10MPa, preferably 7.5-10MPa, more preferably 10MPa; the secondary pressure/total pressure of the dynamic ultrahigh pressure jet is 10-20%.
In the third step of the method provided by the invention, the collision nozzles of the dynamic ultrahigh pressure jet collision method adopt coaxial equal-quantity (0 DEG) collision nozzles, the apertures of the nozzles are the same, the aperture range is 0.1-0.4mm, the jet hole distance is 2-10mm, and the pressure fluctuation in the collision process is kept +/-5 MPa. Wherein, in the third step, the temperature is raised to 28-80 ℃ for the raw milk after energy release.
In the fourth step of the method provided by the invention, the sample injection temperature of raw milk is increased by 10-30 ℃ before heat treatment and sterilization are kept;
the low-temperature heat treatment refers to sterilization at 72-85 ℃ for 12-15s and cooling at 2-6 ℃.
The fourth step of the invention is to increase the sampling temperature by 10-30 ℃ as an essential procedure, and the sampling temperature is obtained by optimizing according to the total pressure range of the ultrahigh-pressure jet flow.
According to the environmental conditions in the method provided by the invention, the environmental temperature of the dynamic ultrahigh pressure jet collision is 20-26 ℃, the environmental humidity is 30-70%, and the total number of bacterial colonies required by air sedimentation microorganisms is less than or equal to 50 CFU/dish.
The equipment conditions in the method provided by the invention are that the dynamic ultrahigh pressure equipment is resistant to Gao Wen ℃ and the pressure resistance is less than or equal to 400MPa.
Under other conditions in the method provided by the invention, the total hardness (CaCO) of the ice water for circulating cooling 3 Meter is less than or equal to 450) mg/L.
Specifically, the invention provides a preparation method for prolonging the shelf life of fresh milk, which comprises the following steps:
(1) Purifying milk: centrifuging raw milk to remove milk; the temperature of the clean milk is 2-6 ℃;
(2) And (3) sterilizing and centrifuging: preheating the raw milk after milk purification, sterilizing, centrifuging, separating and cooling; the water pressure of the degerming centrifugation is 2-5bar, the inlet pressure is 2-6bar, the outlet pressure is 2-6bar, the pressure of compressed air is 6-8bar, the separation temperature is 50-55 ℃, the water pressure is less than or equal to 2.5bar when deslagging, the separation rotating speed is 4000-7000rpm, and the cooling is carried out to 2-6 ℃.
(3) High pressure pump energy storage: performing high-pressure pump energy storage on the cooled raw milk, and removing high-pressure pulses; the energy storage pressure of the high-pressure pump is 50-350, and the secondary pressure is 5-10MPa; the high-pressure pump energy storage uses 38.5kW/380V alternating current, and the pressurizing time is less than or equal to 30s.
(4) Clash heating: the energy is released by collision to the raw milk after the high-pressure pump stores energy, and the temperature is raised at the same time; the collision energy release nozzles are coaxial equal-quantity (0 DEG) collision nozzles, the symmetrical nozzles are identical in aperture, the aperture range is 0.1-0.4mm, and the jet hole distance is 2-10mm; the pressure fluctuation in the collision process is kept +/-5 MPa. The temperature rise after collision is 28-80 ℃.
(5) Sterilizing: before heat treatment and sterilization, the sample injection temperature of the raw milk is increased by 10-30 ℃. Carrying out low-temperature heat treatment on the heated raw milk; the low-temperature heat treatment temperature is 72-85 ℃ and the sterilization time is 12-15s.
(6) And (3) cooling: cooling the sterilized raw milk;
(7) And (3) filling: and filling the cooled raw milk.
In the step (3), preferably, the high-pressure pump energy storage pressure is 150-250, and the secondary pressure is 7.5-10MPa.
In the step (3), more preferably, the high-pressure pump has an accumulated pressure of 200/10MPa (which means a primary pressure of 200MPa and a secondary pressure of 10 MPa)
In the step (6), the cooling temperature is 2-6 ℃.
In the step (7), ultra-clean filling or aseptic filling is adopted for filling.
The raw milk is raw milk, defatted milk or formula milk.
When the invention adopts a single ultrahigh pressure jet method for sterilization, the alkaline phosphatase detection is positive, which indicates that the process can not completely kill pathogenic bacteria in milk when being used alone; after the combined process is adopted for treatment, alkaline phosphatase detection is negative, and lactoperoxidase detection is positive, so that the combined process can completely kill pathogenic bacteria in milk, effectively retain the nutritional ingredients of raw milk, and remarkably prolong the shelf life of the raw milk.
The invention has the excellent effects that:
1. the invention is different from the traditional heat treatment sterilization process, adopts the process of combining ultra-high pressure jet collision with low-temperature heat treatment, can ensure sterilization and in-cell alkaline phosphatase and can also ensure low inherent enzyme inactivation rate of dairy products.
In the previous research, the applicant found that when the ultrahigh pressure jet pressure reaches more than 250MPa, the taste of raw milk can be deteriorated, so that the pressure is strictly controlled below 250MPa, so that not only can the sufficient sterilization rate be ensured, but also the taste of the product can be ensured, and meanwhile, the activity of lactoperoxidase can be kept to be more than 80%. Such pressures are relatively low compared to >400MPa for static ultra-high pressures, and are instantaneously pressurized and instantaneously depressurized without a pressure maintenance process, so that the denaturation rate of proteins and fats is also low, and the retention rate of active proteins and the like is also high.
In the fourth step of the invention, the heated raw milk is subjected to low-temperature heat treatment, namely, in the operation of the step (5), in order not to damage the taste of the milk and to better deactivate enzymes, the invention does not use high temperature, but rather uses relatively mild enzyme deactivation temperature, thereby not only having excellent sterilization and enzyme deactivation effects, but also ensuring that the unique flavor of the milk is not lost.
2. Under the condition that the terminal cold chain piece meets, the shelf life of the fresh milk prepared by the method can be prolonged to more than 20 days relative to 3-7 days of high-temperature short-time pasteurization.
3. In the invention, the heating time of the raw milk in the whole production period (all steps) is more than 50 ℃ and less than 15s, so that the heat load can be reduced to the maximum extent, the flavor and nutrition of the produced fresh milk are ensured, meanwhile, the bad flavor of the pasteurized milk is eliminated, the fishy smell, silage smell and the like are similar, and the high-content nutrient substances are maintained.
4. In the method, the pressure required by ultrahigh pressure jet sterilization is low, the operation is simple and convenient, the continuous production can be realized, the method is easy to connect with the existing process links of a pretreatment system, a sterilization system, a filling system, a packaging system and the like in a factory, and the industrialized production can be realized quickly and efficiently.
Detailed Description
The following examples are illustrative of the invention and are not intended to limit the scope of the invention.
The alkaline phosphatase detection method adopts a NY/T3799 method, and the lactoperoxidase detection method refers to industry standard T/TDSTIA001-2021 'determination of lactoperoxidase in milk and milk products'. In this example, the standard for the acidity and the total number of colonies of fresh milk are evaluated according to the requirements of the national food safety standard pasteurized milk of GB 19645-2010. The fat detection method is carried out by referring to GB 5009.6 third French standard refinement detection fat operation instruction, the protein detection method is carried out by referring to Kjeldahl nitrogen determination method detection protein operation instruction, the non-fat milk solid detection method is carried out by referring to GB 5413.39-2010 national standard refinement detection dry matter (total solids) and non-fat milk solid operation instruction, and the acidity detection method is carried out by referring to GB 5009.239 first French standard refinement detection acidity operation instruction and GB 5009.239 third French standard refinement detection acidity operation instruction.
The specific techniques or conditions are not identified in the examples and are described in the literature in this field or are carried out in accordance with the product specifications. The reagents or equipment used were conventional products available for purchase by regular vendors without the manufacturer's attention.
Example 1
The embodiment provides a method for prolonging the shelf life of fresh milk, which also ensures that the effective nutrient components and the flavor of raw milk are maintained in the fresh milk.
(1) Purifying milk: centrifuging raw milk to clean milk, and cooling to 6deg.C;
(2) And (3) sterilizing and centrifuging: preheating raw milk after purifying milk, performing degerming centrifugation, wherein the water pressure of degerming centrifugation is 5bar, the inlet pressure is 6bar, the outlet pressure is 6bar, the compressed air pressure is 8bar, the separation temperature is 50 ℃, the water pressure is 2.5bar during deslagging, the separation rotating speed is 4200rpm, and cooling to 6 ℃;
(3) High pressure pump energy storage: the cooled raw milk is subjected to high-pressure pump energy storage, the pressure parameter is that the primary pressure is 150MPa, the secondary pressure is 10MPa, and high-pressure pulses are removed; the high-pressure energy storage pump uses 38.5kW/380V alternating current, and the pressurizing time is less than or equal to 30s;
(4) Clash heating: the energy is released by collision to the raw milk after the high-pressure pump stores energy, the aperture range is 0.3mm, the jet hole distance is 3mm, and the pressure fluctuation in the collision process is kept +/-5 MPa;
(5) Sterilizing: carrying out low-temperature heat treatment on the heated raw milk, wherein the sterilization temperature is 75 ℃, and the sterilization time is 12s;
(6) And (3) cooling: the cooling condition is conventional in the art, and the homogenized raw milk is cooled to 6 ℃;
(7) And (3) filling: and (3) filling the cooled raw milk, wherein ultra-clean filling or aseptic filling is adopted for filling, and the temperature of the final product is reduced to 6 ℃.
Example 2
The embodiment provides a method for prolonging the shelf life of fresh milk, which also ensures that the effective nutrient components and the flavor of raw milk are maintained in the fresh milk.
(1) Purifying milk: centrifuging raw milk to clean milk, and cooling to 6deg.C;
(2) And (3) sterilizing and centrifuging: preheating raw milk after purifying milk, performing degerming centrifugation, wherein the water pressure of degerming centrifugation is 5bar, the inlet pressure is 6bar, the outlet pressure is 6bar, the compressed air pressure is 8bar, the separation temperature is 50 ℃, the water pressure is 2.5bar during deslagging, the separation rotating speed is 4200rpm, and cooling to 6 ℃;
(3) High pressure pump energy storage: the cooled raw milk is subjected to high-pressure pump energy storage, the pressure parameter is that the primary pressure is 150MPa, the secondary pressure is 10MPa, and high-pressure pulses are removed; the high-pressure energy storage pump uses 38.5kW/380V alternating current, and the pressurizing time is less than or equal to 30s;
(4) Clash heating: the energy is released by collision to the raw milk after the high-pressure pump stores energy, the aperture range is 0.3mm, the jet hole distance is 3mm, and the pressure fluctuation in the collision process is kept +/-5 MPa;
(5) Sterilizing: carrying out low-temperature heat treatment on the heated raw milk, wherein the sterilization temperature is 75 ℃, and the sterilization time is 15s;
(6) And (3) cooling: the cooling condition is conventional in the art, and the homogenized raw milk is cooled to 6 ℃;
(7) And (3) filling: and (3) filling the cooled raw milk, wherein the filling adopts ultra-clean filling or aseptic filling, and the temperature of the final product is reduced to 6 ℃.
Example 3
The embodiment provides a method for prolonging the shelf life of fresh milk, which also ensures that the effective nutrient components and the flavor of raw milk are maintained in the fresh milk.
(1) Purifying milk: centrifuging raw milk to clean milk, and cooling to 6deg.C;
(2) And (3) sterilizing and centrifuging: preheating raw milk after purifying milk, performing degerming centrifugation, wherein the water pressure of degerming centrifugation is 5bar, the inlet pressure is 6bar, the outlet pressure is 6bar, the compressed air pressure is 8bar, the separation temperature is 50 ℃, the water pressure is 2.5bar during deslagging, the separation rotating speed is 4200rpm, and cooling to 6 ℃;
(3) High pressure pump energy storage: the cooled raw milk is subjected to high-pressure pump energy storage, the pressure parameter is that the primary pressure is 200MPa, the secondary pressure is 10MPa, and high-pressure pulses are removed; the high-pressure energy storage pump uses 38.5kW/380V alternating current, and the pressurizing time is less than or equal to 30s;
(4) Clash heating: the energy is released by collision to the raw milk after the high-pressure pump stores energy, the aperture range is 0.3mm, the jet hole distance is 3mm, and the pressure fluctuation in the collision process is kept +/-5 MPa;
(5) Sterilizing: carrying out low-temperature heat treatment on the heated raw milk, wherein the sterilization temperature is 75 ℃, and the sterilization time is 15s;
(6) And (3) cooling: the cooling condition is conventional in the art, and the homogenized raw milk is cooled to 6 ℃;
(7) And (3) filling: and (3) filling the cooled raw milk, wherein the filling adopts ultra-clean filling or aseptic filling, and the temperature of the final product is reduced to 6 ℃.
Example 4
The embodiment provides a method for prolonging the shelf life of fresh milk, which also ensures that the fresh milk maintains the effective nutrient components and the flavor of raw milk.
(1) Purifying milk: centrifuging raw milk to clean milk, and cooling to 6deg.C;
(2) And (3) sterilizing and centrifuging: preheating raw milk after purifying milk, performing degerming centrifugation, wherein the water pressure of degerming centrifugation is 5bar, the inlet pressure is 6bar, the outlet pressure is 6bar, the compressed air pressure is 8bar, the separation temperature is 50 ℃, the water pressure is 2.5bar during deslagging, the separation rotating speed is 4200rpm, and cooling to 6 ℃;
(3) High pressure pump energy storage: the cooled raw milk is subjected to high-pressure pump energy storage, the pressure parameter is that the primary pressure is 200MPa, the secondary pressure is 10MPa, and high-pressure pulses are removed; the high-pressure energy storage pump uses 38.5kW/380V alternating current, and the pressurizing time is less than or equal to 30s;
(4) Clash heating: the energy is released by collision to the raw milk after the high-pressure pump stores energy, the aperture range is 0.3mm, the jet hole distance is 3mm, and the pressure fluctuation in the collision process is kept +/-5 MPa;
(5) Sterilizing: carrying out low-temperature heat treatment on the heated raw milk, wherein the sterilization temperature is 85 ℃, and the sterilization time is 15s;
(6) And (3) cooling: the cooling condition is conventional in the art, and the homogenized raw milk is cooled to 6 ℃;
(7) And (3) filling: and (3) filling the cooled raw milk, wherein the filling adopts ultra-clean filling or aseptic filling, and the temperature of the final product is reduced to 6 ℃.
Experimental example 1
Shelf life analysis of the products produced in each example is shown in Table 1.
TABLE 1 shelf life experiment of fresh milk Cold storage Condition (6 ℃ C.) after filling
Experimental example 2
The microbiological detection data for each example are shown in Table 2. The nutritional data are shown in Table 3.
Table 2 microbiological data for ultra-high pressure jet sterilization process
Table 3 nutrient composition data for ultra high pressure jet sterilization process
Comparative example 1
Based on the embodiment 4, the collision angle in the step (4) is adjusted, and 10 degrees and 20 degrees are selected for gradient test: carrying out low-temperature heat treatment on the heated raw milk, wherein the sterilization temperature is 85 ℃, and the sterilization time is 15s; the starting materials and the remaining steps were the same as in example 4.
Through detection, the total number of finished product bacterial colonies increases along with the increase of the collision angle, the quality guarantee period of the cow milk sample obtained under the treatment condition of comparative example 1 under the low-temperature refrigeration (6 ℃) condition is less than 7 days, the acidity in the shelf life exceeds the national standard requirement (> 18 ℃) of pasteurized milk, the sensory evaluation of the sample is unqualified (the milk flavor is light, the milk has sour odor), the color is off-white, and more coagulum is generated. The invention shows that in the dynamic ultrahigh pressure jet collision process, the angle of the collision nozzle for collision energy release is very critical, and the coaxial equal-quantity (0 ℃) collision nozzle is adopted, so that the sterilization effect is better than that of the nozzle adopting 10 DEG and 20 DEG, and the sterilization is more thorough.
Comparative example 2
On the basis of example 4, the nozzle aperture of step (4) was adjusted and gradient tests were performed by selecting 0.6mm and 0.9 mm: carrying out low-temperature heat treatment on the heated raw milk, wherein the sterilization temperature is 85 ℃, and the sterilization time is 15s; the starting materials and the remaining steps were the same as in example 4.
According to detection, the total number of finished product bacterial colonies increases along with the increase of the aperture of the nozzle, the quality guarantee period of the cow milk sample obtained under the treatment condition of comparative example 2 under the low-temperature refrigeration (4 ℃) condition is less than 7 days, the acidity of the shelf life exceeds the national standard requirement (> 18 ℃) of pasteurized milk, the sensory evaluation of the sample is unqualified (the milk flavor is light, the milk flavor has slight sour odor), the color is off-white, and slight coagulum is generated. This shows that the size of the nozzle aperture is one of the key factors in the dynamic ultra-high pressure jet collision process, and the sterilization effect is best by adopting the nozzle aperture of 0.3 mm.
Comparative example 3
Based on the example 4, the jet hole distance in the step (4) is adjusted, and 13mm and 23mm are selected for gradient test: carrying out low-temperature heat treatment on the heated raw milk, wherein the sterilization temperature is 85 ℃, and the sterilization time is 15s; the starting materials and the remaining steps were the same as in example 4.
According to detection, the total number of finished product bacterial colonies increases along with the increase of the jet hole distance, the quality guarantee period of the cow milk sample obtained under the treatment condition of comparative example 3 under the low-temperature refrigeration (6 ℃) condition is less than 7 days, the acidity in the shelf life exceeds the national standard requirement (> 18 ℃) of pasteurized milk, the sensory evaluation of the sample is disqualified (the milk flavor is light, the cow milk sample has slight sour odor), the color is off-white, and slight coagulum is generated. This shows that in the dynamic ultra-high pressure jet collision process of the invention, the jet hole distance is one of the key factors influencing the sterilization effect, and the sterilization effect is far less than the jet hole distance of 2-10mm by adopting the jet hole distance of more than 10 mm.
Comparative example 4
Based on example 4, the separation temperature in step (2) was adjusted, and gradient test was performed at 40℃and 45 ℃): carrying out low-temperature heat treatment on the heated raw milk, wherein the sterilization temperature is 85 ℃, and the sterilization time is 15s; the starting materials and the remaining steps were the same as in example 4.
According to detection, the total colony count of the finished product increases along with the reduction of the separation temperature, the quality guarantee period of the cow milk sample obtained under the treatment condition of comparative example 4 under the low-temperature refrigeration (6 ℃) condition can reach 10 days, the acidity after 10 days of storage exceeds the national standard requirement (> 18 ℃) of pasteurized milk, the sensory evaluation of the sample is unqualified (the milk flavor is light, the cow milk sample has slight sour odor), the color is off-white, and slight coagulum is generated.
Comparative example 5
On the basis of example 4, the separation rotation speed in the step (2) is adjusted, and 3800rpm and 4000rpm are selected for gradient test: carrying out low-temperature heat treatment on the heated raw milk, wherein the sterilization temperature is 85 ℃, and the sterilization time is 15s; the starting materials and the remaining steps were the same as in example 4.
According to detection, the total number of finished product bacterial colonies increases along with the reduction of the separation rotating speed, the quality guarantee period of the cow milk sample obtained under the treatment condition of comparative example 5 under the low-temperature refrigeration (6 ℃) condition can reach 12 days, the acidity after 12 days of storage exceeds the national standard requirement (> 18 ℃) of pasteurized milk, the sensory evaluation of the sample is unqualified (the milk flavor is light, the milk flavor has slight sour odor), the color is off-white, and slight coagulum is generated.
Comparative example 6
On the basis of example 1, step (5) was omitted, and in step (3), the homogenization pressure of different levels as in Table 4 was selected, and the other steps were the same as in example 1, and the nutrient composition data of the fresh milk obtained are shown in Table 4.
TABLE 4 Table 4
Pressure (MPa)
|
Furoic acid (mg/100 g protein)
|
Alkaline phosphatase
|
Lactoperoxidase
|
Raw milk
|
5.8
|
Positive and negative
|
10236
|
50
|
5.5
|
Positive and negative
|
7693
|
100
|
4.4
|
Positive and negative
|
9044
|
150
|
4.6
|
Positive and negative
|
7220
|
200
|
4.4
|
Positive and negative
|
8011
|
250
|
5.0
|
Positive and negative
|
8792
|
300
|
6.4
|
Positive and negative
|
7926 |
While the invention has been described in detail in the foregoing general description and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that modifications and improvements can be made thereto. Accordingly, such modifications or improvements may be made without departing from the spirit of the invention and are intended to be within the scope of the invention as claimed.